Bromine-impregnated activated carbon and process for preparing the same

ABSTRACT

A bromine-impregnated activated carbon wherein the contents of any alkali metal, any alkali earth metal and iron are not higher than 0.3 wt % and the content of bromine is not lower than 3 wt %, with respect to the weight of a material activated carbon. The bromine-impregnated activated carbon has improved adsorption characteristics to the alkyl sulfides, which have not been sufficiently removed by activated carbons prepared by the conventional techniques. Further, variations in the absorption characteristics can be reduced and the activated carbon can exhibit a stable performance in removing the alkyl sulfides.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application is related to Japanese applications Nos. Hei9(1997)-200371 and Hei 9(1997)-297440 filed on Jul. 25, 1997 and Oct.29, 1997 respectively, whose priorities are claimed under 35 USC § 119,the disclosures of which are incorporated by reference in theirentirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a bromine-impregnated activatedcarbon and a process for preparing the same. More particularly, thebromine-impregnated activated carbon is used for removing alkyl sulfidesfrom gas containing the alkyl sulfides in small concentrations.

[0004] 2. Description of Related Art

[0005] Sulfur compounds such as hydrogen sulfide, mercaptans and alkylsulfides are contained in exhaust gas from sewage treatment plants, rawsewage treatment plants, waste disposal plants, and process gas andexhaust gas from chemical plants for petroleum refining, petroleumchemistry, paper pulp production and the like and from food processingplants.

[0006] Various methods for removing sulfur compounds contained in suchgases are conventionally known, including an alkali absorbing method, awet oxidation method, an ozone oxidation method, an activated carbonadsorption method and a combustion method, for example.

[0007] These conventional methods are useful for removing many kinds ofsulfur compounds. However, alkyl sulfides such as dimethyl sulfide anddimethyl disulfide, which are specific smelly substances, cannot beremoved to a satisfactory extent by the conventional methods.

[0008] Under these circumstances, Japanese Unexamined PatentPublications Nos. Sho 54(1979)-132470, Sho 50(1975)-130679 and Sho55(1980)-51422, for example, propose that dimethyl sulfide and dimethyldisulfide can be removed by chemical adsorption by using abromine-impregnated activated carbon instead of an usual activatedcarbon in the adsorption method. The chemical adsorption is a mechanismdifferent from physical adsorption by the usual activated carbon.

[0009] Surely, in the case where the bromine-impregnated activatedcarbon is used, specific smelly substances such as dimethyl sulfide anddimethyl disulfide can be more effectively removed than the conventionalactivated carbon. However, the bromine-impregnated activated carbondiffer in quality depending upon various parameters such as the amountof bromine carried by the activated carbon. Accordingly, in the presentsituation, dimethyl sulfide and dimethyl disulfide cannot always beremoved to a satisfactory degree.

SUMMARY OF THE INVENTION

[0010] The present invention provides a bromine-impregnated activatedcarbon wherein the contents of any alkali metal, any alkali earth metaland iron are not higher than 0.3 wt % and the content of bromine is notlower than 3 wt %.

[0011] Further, the present invention provides a process for preparingthe bromine-impregnated activated carbon comprising the steps of:reducing the contents of any alkali metal, any alkali earth metal andiron in a material activated carbon to 0.3 wt % or lower; andimpregnating the activated carbon with bromine such that the content ofbromine is not lower than 3 wt %.

[0012] In another aspect, the present invention provides abromine-impregnated activated carbon, wherein the content of a surfaceoxide is not higher than 2.5 wt % in terms of oxygen and the activatedcarbon is impregnated with bromine such that the content of bromine isnot lower than 3 wt %.

[0013] Further, the present invention provides a process for preparingthe bromine-impregnated activated carbon of the above comprising thesteps of: thermally treating a raw material activated carbon at 500° C.to 1,100° C. in the absence of oxygen to produce a carrier activatedcarbon; and impregnating the carrier activated carbon with bromine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] As a material activated carbon for producing thebromine-impregnated activated carbon of the present invention, usable isany activated carbon prepared from a raw material such as coal, coke,charcoal, coconut shell, resin, petroleum residuum or the like by aknown process that has a specific surface area of about 100 m²/g to2,000 m²/g. The material activated carbon may be in any form such asspherical, cylindrical, crushed, powdery, granular, fibriform orhoneycombed form.

[0015] The alkali metals and alkali earth metals whose contents in thebromine-impregnated activated carbon of the present invention arecontrolled include Na, K, Mg, Ca, Zn and the like, for example. Inwhatever form these metals may be present, e.g., in a free form or inthe form of a compound such as an oxide, a carbonate or a chloride, thecontents thereof in terms of metals is preferably about 0.3 wt % orlower, more preferably about 0.1 wt % or lower, still more preferablyabout 0.05 wt % or lower, with respect to the weight of a materialactivated carbon. Especially, in the cases where the alkali metals andalkali earth metals are in a form which enables them to react withbromine, for example, in a free form, or in the cases where the alkalimetals and alkali earth metals are ready to react with bromine, forexample, in the form of an oxide (hydroxide) or in the form of aniodide, the contents of such metals are preferably about 0.2 wt % orlower in terms of the metals with respect to the weight of the materialactivated carbon.

[0016] The contents of the alkali metals and alkali earth metals arediscussed here in wt % with respect to the material activated carbon.However, as described later, since the impregnation amount of bromine isusually within the range from about 3 wt % to about 50 wt % with respectto the material activated carbon, the contents of the alkali metals andalkali earth metals can be calculated, if necessary, in wt % to thebromine-impregnated activated carbon from the amount of bromine withwhich the bromine-impregnated activated carbon is impregnated. In thiscase, the contents of the alkali metals and the alkali earth metals arepreferably about 0.3 wt % or lower, more preferably about 0.1 wt % orlower, still more preferably about 0.05 wt % or lower, for example, withrespect to the weight of the bromine-impregnated activated carbon.

[0017] The content of iron in the material activated carbon ispreferably about 0.3 wt % or lower, more preferably about 0.1 wt % orlower, still more preferably about 0.05 wt % or lower, and the contentof iron in the bromine-impregnated activated carbon is preferably about0.3 wt % or lower, more preferably about 0.1 wt % or lower, still morepreferably about 0.05 wt % or lower. In the cases where the iron is in aform which enables them to react with bromine or in the cases where theiron is ready to react with bromine, the contents of iron is preferablyabout 0.2 wt % or lower in terms of the metals with respect to theweight of the material activated carbon.

[0018] Further, in the present invention, the bromine-impregnatedactivated carbon having the controlled contents of the alkali metals,alkali earth metals and iron as described above can exhibit moreimproved adsorption characteristics if the content of surface oxides iscontrolled as described below.

[0019] In the bromine-impregnated activated carbon of the presentinvention, the surface oxides whose content is controlled includevarious kinds of oxides such as carbon-oxygen complex (i.e., carbonmonooxide, carbon dioxide), oxides of alkali metals and alkali earthmetals. The content of such oxides is preferably about 2.5 wt % orlower, more preferably about 2 wt % or lower, still more preferablyabout 1.5 wt % or lower, in terms of oxygen with respect to the materialactivated carbon before the impregnation with bromine. In thebromine-impregnated activated carbon of the present invention, oxidativeeffect of bromine leads to oxidation of the activated carbon with time.As a result, the surface oxides tend to increase to some extent.Therefore, the content of the surface oxides in the bromine-impregnatedactivated carbon as finally obtained is controlled as discussed above interms of weight with respect to the material activated carbon before theimpregnation with bromine. In this case, the contents of the alkalimetals and the like are preferably controlled, but the content of thesurface oxides does not necessarily have relation with the contents ofthe alkali metals and the like.

[0020] The content of bromine in any bromine-impregnated activatedcarbon accordingly to the present invention is preferably about 3 wt %or higher, more preferably about 5 wt % or higher, still more preferablyabout 5 wt % or higher and about 50 wt % or lower, most preferably about5 wt % or higher and about 20 wt % or lower, with respect to thematerial activated carbon before the impregnation with bromine.

[0021] According to the present invention, a method of reducing thecontents of the alkali metals and alkali earth metals in the materialactivated carbon to about 0.3 wt % or lower is not particularly limited.Examples of such treatment methods include a method of dipping thematerial activated carbon in water or an acid solution, e.g., about 1 toabout 10 wt % hydrochloric acid, phosphoric acid, nitric acid, sulfuricacid and organic acid (e.g., formic acid, acetic acid, oxalic acid andthe like), and allowing to stand, stirring and/or boiling for a certaintime period (e.g., for about 0.1 to about one hour); a method of feedingwater or an acid solution into the material activated carbon for acertain time period (e.g., about one to about ten hours) with stirringthe material activated carbon; and a method of passing water or an acidsolution through a layer of the material activated carbon. Thesetreatments may be carried out once or repeated twice or more. In thecase where the material activated carbon is treated with the acidsolution, the treatment is preferably followed by washing with waterabout one to about five times. In the case where the alkali metals andalkali earth metals can be removed (or deactivated) sufficiently only bywashing with water, the contents of the alkali metals and alkali earthmetals may be reduced to about 0.3 wt % or lower only by washing withwater.

[0022] In the process for preparing the bromine-impregnated activatedcarbon of the present invention, in order to keep the content of thesurface oxides in the bromine-impregnated activated carbon as finallyobtained within the aforesaid range, the content of the surface oxidesin the material activated carbon before the impregnation with bromine ispreferably about 2.0 wt % or lower, more preferably about 1.5 wt % orlower, still preferably about 1.0 wt % or lower, in terms of oxygen.

[0023] In the process for preparing the bromine-impregnated activatedcarbon of the present invention, the content of the surface oxides inthe carrier activated carbon before the impregnation with bromine may bereduced to about 2.0 wt % in terms of oxygen by thermally treating thematerial activated carbon at 500 to 1,100° C. in the absence of oxygen,for example. This thermal treatment can be performed by various methodssuch as a high-temperature pyrolysis method and a high-temperaturehydrogen reduction method. Alternatively, a liquid-phase reductionmethod may be utilized besides the thermal treatment in the absence ofoxygen, for example. However, for controlling the content of the surfaceoxides in the material activated carbon efficiently, thehigh-temperature pyrolysis method and the high-temperature hydrogenreduction method are preferred.

[0024] The high-temperature pyrolysis method is a method of thermallytreating the material activated carbon in an inert gas such as nitrogengas, argon gas or the like which does not contain oxygen or in vacuum tothermally decompose oxides. As for temperature for the thermaltreatment, the higher, the more efficient. However, since some activatedcarbons used as the material activated carbon have their pores closed attemperatures over about 1,200° C., the thermal treatment temperature issuitably about 500° C. to about 1,100° C., preferably about 700° C. toabout 950° C. A treatment time period can be decided as requiredaccording to the amount of the material activated carbon to be treated,and for example, the treatment time period is about 0.1 to about 10hours.

[0025] The high-temperature hydrogen reduction method is a method ofthermally treating the material activated carbon in an atmosphere of gascontaining hydrogen to reduce oxides, for example. Temperature for thisthermal treatment is suitably about 400° C. to about 1,000° C.,preferably about 500° C. to about 850° C., more preferably around 700°C. A treatment time period is suitably about 0.1 to about 10 hours.

[0026] The liquid-phase reduction method is a method of dipping ormixing/stirring the material activated carbon in a reducing solvent, forexample, of hydrazine within the temperature range from room temperatureto about 100° C.

[0027] One of the above treatment methods may be performed once orrepeated twice or more, or different ones of the above treatment methodsmay be combined in a multi-stage treatment.

[0028] Any bromine-impregnated activated carbon according to the presentinvention can be impregnated with bromine by a per-se known method. Forexample, the impregnation can be performed by a gas-phase impregnationmethod of contacting a carrier gas containing bromine gas with theactivated carbon treated desirably, by a liquid-phase impregnationmethod of dipping the treated activated carbon in bromine water, and aspray impregnation method of spraying liquid bromine directly onto thetreated activated carbon for impregnation.

[0029] Usually, in the gas-phase impregnation method, air, nitrogen gas,carbon dioxide, carbon monooxide or the like is used as the carrier gas,a contact temperature is set at about 150° C. or lower, preferably about80° C. or lower, and bromine impregnation is continuously carried outusing a fluidized bed, moving bed or spraying and mixing bed of theactivated carbon, for example. In this method, after the activatedcarbon is impregnated with bromine by passing the bromine-containinggas, it is preferable to pass the carrier gas alone to remove remainingbromine gas.

[0030] In the liquid-phase impregnation method, the activated carbon isdipped in bromine water containing about 1% to about 5% bromine forabout one to about ten hours. Or bromine water is passedthrough/contacted with the activated carbon using a fluid bed, movingbed, fixed bed or spray bed of the activated carbon to impregnate theactivated carbon with bromine, followed by separation by filtration anddrying. Temperature for this method is preferably about 80° C. or lower,still more preferably about 50° C. or lower.

[0031] In the method of spraying liquid bromine for impregnation, liquidbromine, bromine water or the like is sprayed onto the treated activatedcarbon with stirring the activated carbon, followed by drying, ifnecessary. Contact temperature for this method is preferably about 50°C. or lower.

[0032] In order to adsorb/remove alkyl sulfides, especially dimethylsulfide and dimethyl disulfide, from gas containing the alkyl sulfideswith the bromine-impregnated activated carbon of the present invention,the gas to be treated may be contacted with the bromine-impregnatedactivated carbon by a known method such as a fixed bed, a moving bed, afluid bed, a slurry-type or a batch-type contact stirring method, forexample. A contact time period in this case can be varied as necessaryaccording to the concentration of the alkyl sulfides, the particle sizeof the bromine-impregnated activated carbon used, the contact method andthe like, but usually for about 0.1 seconds to about one minutes atabout 50° C. or lower.

[0033] Now described are preparation examples and application examplesof the bromine-impregnated activated carbon of the present invention.

REFERENCE EXAMPLE: ARBITRARILY SELECTED ACTIVATED CARBON Preparation ofBromine-impregnated Activated Carbons

[0034] Activated carbon samples whose raw materials and properties areshown in Table 1 were dried in an air bath at 115° C. for three hours byan electric drier, and then cooled to room temperature in a desiccator.The samples were collected 100 g each.

[0035] Subsequently, each of the activated carbon samples was put in athree-liter glass conical flask. A layer of the activated carbon wasflattened, on which three grams of silica wool was put. Then, ten gramsof bromine of guaranteed reagent grade was dropped onto the silica wool,and the flask was shook and stirred to impregnate the activate carbonwith vaporized bromine gas. Thus, Samples A to C were prepared. Theimpregnation amount of bromine was calculated by an increase of theweight of the sample collected after all bromine got carried by theactivated carbon and the gas within the flask turned colorless andtransparent. TABLE 1 Impregnation Sample No. BET Amount of (ReferenceMain Raw Surface Area Bromine Example) Form Material (m²/g) (g/100 g) A4 to 8 mesh Coconut Shell 1010 9.8 Crushed B 4 mm φ Coconut Shell 12009.8 Cylindrical C 4 mm φ Bituminous 1210 9.7 Cylindrical Coal

Dimethyl Sulfide Adsorption Characteristics

[0036] The bromine-impregnated activated carbons thus obtained werecrushed and sieved with a 16 to 24 mesh and fed in glass columns of 15.6mm inner diameter to form layers of 100 mm height (19.1 ml). Air havinga relative humidity of 80% which contains 3 ppm dimethyl sulfide waspassed at 40 cm/sec in the columns at 25° C.

[0037] The concentration (C) of dimethyl sulfide in the air at an outletof each of the activated carbon layers and the concentration (C₀) ofdimethyl sulfide in the air at an inlet to each of the activated carbonlayers were measured by a gas chromatograph provided with an FPDdetector. Time having passed until a breakthrough ratio C/C₀ reached0.05 was counted for each of the activated carbons (as a breakthroughtime). The results are shown in Table 2.

[0038] For comparison, the breakthrough time concerning dimethyl sulfidewas counted using the respective bromine-unimpregnated activated carbons(A′, B′, C′) in the same manner. The results are also shown in Table 2.TABLE 2 Sample Breakthrough Time Sample Breakthrough Time No. (hrs) No.(hrs) A 15.5 A′ 3.0 B 6.5 B′ 4.0 C 35.0 C′ 3.5

Analysis of Activated Carbons

[0039] Ash of the respective activated carbons was mixed with lithiumborate and melted, and then dissolved in dilute nitric acid. Thecontents of Na, K, Mg, Ca, Zn, Fe and Cu, which are likely to formbromides and usually are contained in activated carbons, were determinedby Atomic Absorption Spectrometry. The results are shown in Table 3.TABLE 3 (g/100 g) A′ B′ C′ Na 0.17 0.25 0.025 K 1.33 1.02 0.045 Mg 0.0490.29 0.065 Ca 0.046 0.16 0.25 Zn 0.003 0.005 0.005 Fe 0.006 0.20 0.75 Cu0.003 0.004 0.001

EXAMPLE 1: ACID-WASHED ACTIVATED CARBONS Washing of Activated Carbons

[0040] A chloric acid of 5 wt %, 1,000 g, was added to 200 g of each ofthe respective bromine-unimpregnated activated carbons A′, B′ and C′used in the above Reference example. The resulting mixtures were boiledfor 30 minutes and then the washing liquid was removed. Further,ion-exchange water was added thereto and then replacement ofion-exchange water was repeated five times. The resulting activatedcarbons after washing are referred to as A-1′, B-1′ and C-1′.

[0041] Further, the bromine-unimpregnated activated carbon A′ and C′were washed only with ion-exchange water instead of chloric acid. Theresulting activated carbons are referred to as A-2′ and C-2′.

Preparation of Bromine-Impregnated Activated Carbons

[0042] The washed activated carbons obtained as described above weredried sufficiently and made into bromine-impregnated activated carbons(A-1, A-2, B-1, C-1 and C-2) as shown in Table 4 in the same manner asin Reference Example. TABLE 4 BET Impregnation Sample Surface Amount ofNo. Area Bromine (Example) Washing Main Material (m²/g) (g/100 g) A-1Chloric acid - Coconut Shell 1025 9.7 Ion-exchange water A-2Ion-exchange Coconut Shell 1020 9.8 water B-1 Chloric acid - CoconutShell 1235 9.8 Ion-exchange water C-1 Chloric acid - Bituminous 1230 9.6Ion-exchange water Coal C-2 Ion-exchange water Bituminous 1220 9.7 Coal

Dimethyl Sulfide Adsorption Characteristics

[0043] The dimethyl sulfide breakthrough time was counted for theprepared bromine-impregnated activated carbons in the same manner as inthe Reference Example. The results are shown in Table 5.

[0044] The dimethyl sulfide breakthrough time was also counted for thecorresponding bromine-unimpregnated samples (A-1′, A-2′, B-1′, C-1′ andC-2′) in the same manner for control. The results are also shown inTable 5. TABLE 5 Sample No. Breakthrough Time Sample No. BreakthroughTime (Example) (hrs.) (for control) (hrs.) A-1 233.0 A-1′ 3.0 A-2 170.0A-2′ 3.0 B-1 245.0 B-1′ 4.0 C-1 243.0 C-1′ 3.5 C-2 175.0 C-2′ 3.5

Analysis of Activated Carbons

[0045] Ash of each of the bromine-unimpregnated activated carbons (A-1′,A-2′, B-1′, C-1′ and C-2′) was analyzed on the contents of Na, K, Mg,Ca, Zn, Fe and Cu in the same manner as in the Reference Example. Theresults are shown in Table 6. TABLE 6 (g/100 g) A-1′ A-2′ B-1′ C-1′ C-2′Na 0.012 0.015 0.013 0.004 0.017 K 0.027 0.13 0.025 0.005 0.008 Mg 0.0050.015 0.004 0.007 0.031 Ca 0.004 0.040 0.009 0.020 0.13 Zn <0.001 0.002<0.001 <0.001 0.004 Fe 0.001 0.005 0.019 0.025 0.25 Cu 0.001 0.003 0.0020.001 0.001

EXAMPLE 2 Thermal Treatment of Activated Carbons

[0046] Activated carbons whose raw materials and properties are shown inTable 7, each 300 g, were thermally treated by a ring furnace at 850° C.with a flow of nitrogen at 5 liter/minute for 30 minutes. After thethermal treatment, the activated carbons were cooled with nitrogen gas.

Preparation of Bromine-impregnated Activated Carbons

[0047] The thermally treated activated carbons were dried by theelectric drier at 115° C. for three hours, and then cooled to roomtemperature in the desiccator. The resulting activated carbons werecollected 100 g each.

[0048] Subsequently, each of the activated carbons were put in aone-liter glass conical flask. About three grams of silica wool were puton flattened layers of the activated carbons, and then ten grams ofbromine of the guaranteed reagent grade were dropped onto the silicawool. The flask was shook and stirred to impregnate the activated carbonsamples with bromine. Thus, Samples D to F were prepared. Theimpregnation amount of bromine was calculated from an increase of theweight of the sample collected after the inside of the flask becamecolorless and transparent, and are shown in Table 7. TABLE 7 BET SurfaceImpregnation Main Area Amount of Bromine Sample Form Material (m²/g)(g/100 g) D 4 mm φ Coconut 1232 9.3 Cylindrical Shell E 4 mm φ Coal A1245 9.4 Cylindrical F 4 mm φ Coal B 1163 9.2 Cylindrical

Dimethyl Sulfide Adsorption Characteristics

[0049] The bromine-impregnated activated carbons (Samples D to F)obtained as described above were crushed and sieved with the 16 to 24mesh and put in glass columns having an inner diameter of 15.6 mm inlayers of 100 mm thickness (19.1 ml). Air having a relative humidity of80% which contained 3 ppm dimethyl sulfide was passed in the columns ata flow rate of 40 cm/sec at 25° C.

[0050] The time (the breakthrough time) having passed until thebreakthrough ratio C/C₀ reached 0.05 was counted in the same matter asin Reference Example 1. The results are shown in Table 8. TABLE 8Samples Breakthrough Time (hrs) D 400 E 405 F 395

Determination of Surface Oxides in Activated Carbons

[0051] Samples of the respective bromine-impregnated activated carbons,3 g each, were put in quartz columns of φ20×1,000 mm. The samples werefixed by sufficiently dried glass wool at their fronts and backs. Thecolumns were set in an electric ring furnace. The columns were closedwith rubber caps, which were provided with openings for letting nitrogengas into the columns and openings for letting nitrogen gas out of thecolumns. The columns were heated to 100° C. with nitrogen gas beingflown into the columns at a flow rate of 100 ml/minute. Subsequently,gas coming out of outlets was sent to two-liter tetra pak® and heated to900° C. at a rate of 400° C. /hour. When reached 900° C., thetemperature was maintained at 900° C. for 30 minutes. Then, the tetrapak® were taken off. The amount of collected gas was measured, and thetotal concentration of CO and CO₂ in the collected gas was determined bythe gas chlomatograph with the FID detector provided with a methaneconberter. Then the content of the surface oxides was calculated interms of oxygen. Also, the content of surface oxides in thebromine-unimpregnated activated carbons before the impregnation withbromine was determined and calculated in the same way as D″,E″,F″. Theresults are shown in Table 9. TABLE 9 (mg/g) Content of Surface OxidesSamples in Terms of Oxygen D 9.3 E 8.29 F 10.21 D″ 2.39 E″ 2.03 F″ 2.62

[0052] The activated carbons of Samples D to F had the contents ofalkali metals and the like shown in Table 10. TABLE 10 (g/100 g) D E FNa 0.011 0.022 0.02 K 0.023 0.02 0.021 Mg 0.006 0.025 0.05 Ca 0.006 0.110.21 Zn 0.001 0.003 0.003 Fe 0.016 0.21 0.23 Cu 0.001 0.001 0.001

EXAMPLE 3 Preparation of Bromine-Impregnated Activated Carbon

[0053] Activated carbons which were not subjected to the thermaltreatment but had the contents of alkali metals and the like shown inTable 12 were modified into bromine-impregnated activated carbons in thesame manner as in Example 2. The results are shown in Table 11. TABLE 11Impregnation Amount Main BET Surface of Bromine Sample Form MaterialArea (m²/g) (g/100 g) D′ 4 mm φ Cylindrical Coconut 1225 9.4 E′ 4 mm φCylindrical Coal A 1203 9.2 F′ 4 mm φ Cylindrical Coal B 1131 9.6

[0054] TABLE 12 (g/100 g) D′ E′ F′ Na 0.012 0.05 0.018 K 0.03 0.0150.038 Mg 0.002 0.028 0.031 Ca 0.005 0.11 0.13 Zn 0.002 0.003 0.003 Fe0.016 0.21 0.16 Cu 0.001 0.001 0.002

Dimethyl Sulfide Adsorption Characteristics

[0055] The breakthrough time was determined for the bromine-impregnatedactivated carbons obtained as described above (Samples D′ to F′) in thesame manner as in Example 2. The results are shown in Table 13. TABLE 13Samples Breakthrough Time (hrs) D′ 255 E′ 190 F′ 285

Determination of Surface Oxides in Activated Carbons

[0056] Surface oxides in the bromine-impregnated activated carbonsprepared from the activated carbons not having been subjected to thethermal treatment were analyzed in the same manner as in Example 2. Theresults are shown in Table 14. TABLE 14 (g/100 g) Content of SurfaceOxides Samples in Terms of Oxygen D′ 29.02 E′ 50.55 F′ 26.00

[0057] According to the present invention, the bromine-impregnatedactivated carbon has improved adsorption characteristics to the alkylsulfides, which have not been sufficiently removed by activated carbonsprepared by the conventional techniques. Further, variations in theabsorption characteristics can be reduced and the activated carbon canexhibit a stable performance in removing the alkyl sulfides.

1. A bromine-impregnated activated carbon wherein the contents of anyalkali metal, any alkali earth metal and iron are not higher than 0.3 wt% and the content of bromine is not lower than 3 wt %.
 2. Abromine-impregnated activated carbon according to claim 1 in which thecontent of bromine is 50 wt % or lower.
 3. A bromine-impregnatedactivated carbon according to claim 1 in which the content of a surfaceoxide is not higher than 2.5 wt % in terms of oxygen.
 4. A process forpreparing the bromine-impregnated activated carbon comprising the stepsof: reducing the contents of any alkali metal, any alkali earth metaland iron in a material activated carbon to 0.3 wt % or lower; andimpregnating the activated carbon with bromine such that the content ofbromine is not lower than 3 wt %.
 5. A process according to claim 4 ,wherein the contents of any alkali metal, any alkali earth metal andiron in the material activated carbon is reduced to 0.3 wt % or lower bytreating a material activated carbon with water or with an acidicaqueous solution.
 6. A process according to claim 4 , further comprisingthe steps of thermally treating a raw material activated carbon at 500°C. to 1,100° C. in the absence of oxygen to produce a carrier activatedcarbon before the step of impregnating the carrier activated carbon withbromine.
 7. A bromine-impregnated activated carbon, wherein the contentof a surface oxide is not higher than 2.5 wt % in terms of oxygen andthe activated carbon is impregnated with bromine such that the contentof bromine is not lower than 3 wt %.
 8. A bromine-impregnated activatedcarbon according to claim 7 in which the content of bromine is 50 wt %or lower.
 9. A process for preparing the bromine-impregnated activatedcarbon of claim 7 comprising the steps of: thermally treating a rawmaterial activated carbon at 500° C. to 1,100° C. in the absence ofoxygen to produce a carrier activated carbon; and impregnating thecarrier activated carbon with bromine.
 10. A process according to claim9 , wherein the content of a surface oxide in the material activatedcarbon before impregnated with bromine is not higher than 2.0 wt % interms of oxygen.